[llvm] [CodeGen] Parse frame-pointer attribute once when creating MachineFunction (PR #191974)

[Cullen Rhodes via llvm-commits]

https://github.com/c-rhodes created https://github.com/llvm/llvm-project/pull/191974

TargetOptions::DisableFramePointerElim is hot and showing up in compile-time profiles via AArch64FrameLowering::hasFPImpl on aarch64-O0-g builds. Repeatedly looking up the function attribute is expensive. Parsing it once at MachineFunction initialisation and storing as FramePointerKind on MachineFrameInfo is a -0.21% geomean improvement on CTMark stage1-aarch64-O0-g. Also helps debug builds on other targets.

https://llvm-compile-time-tracker.com/compare.php?from=215f35eb8f1c313ac135ad47db1cc0b99b3ae694&to=51f6617517177bea1cc49baeab3acaf62d5e9df9&stat=instructions%3Au

>From 056e2230eca86d1362452178012fb33aeb806362 Mon Sep 17 00:00:00 2001
From: Cullen Rhodes <cullen.rhodes at arm.com>
Date: Mon, 13 Apr 2026 10:13:19 +0000
Subject: [PATCH] [CodeGen] Parse frame-pointer attribute once when creating
 MachineFunction

TargetOptions::DisableFramePointerElim is hot and showing up in
compile-time profiles via AArch64FrameLowering::hasFPImpl on
aarch64-O0-g builds. Repeatedly looking up the function attribute is
expensive. Parsing it once at MachineFunction initialisation and storing
as FramePointerKind on MachineFrameInfo is a -0.21% geomean improvement
on CTMark stage1-aarch64-O0-g. Also helps debug builds on other targets.

https://llvm-compile-time-tracker.com/compare.php?from=215f35eb8f1c313ac135ad47db1cc0b99b3ae694&to=51f6617517177bea1cc49baeab3acaf62d5e9df9&stat=instructions%3Au
---
 llvm/include/llvm/CodeGen/MachineFrameInfo.h | 10 ++++++
 llvm/lib/CodeGen/MachineFunction.cpp         | 17 +++++++++
 llvm/lib/CodeGen/TargetOptionsImpl.cpp       | 37 ++++++++++----------
 3 files changed, 46 insertions(+), 18 deletions(-)

diff --git a/llvm/include/llvm/CodeGen/MachineFrameInfo.h b/llvm/include/llvm/CodeGen/MachineFrameInfo.h
index c4852f84be352..22729e736fbd3 100644
--- a/llvm/include/llvm/CodeGen/MachineFrameInfo.h
+++ b/llvm/include/llvm/CodeGen/MachineFrameInfo.h
@@ -17,6 +17,7 @@
 #include "llvm/CodeGen/Register.h"
 #include "llvm/CodeGen/TargetFrameLowering.h"
 #include "llvm/Support/Alignment.h"
+#include "llvm/Support/CodeGen.h"
 #include "llvm/Support/Compiler.h"
 #include <cassert>
 #include <vector>
@@ -279,6 +280,10 @@ class MachineFrameInfo {
   /// Set to true if this function has any function calls.
   bool HasCalls = false;
 
+  /// Frame-pointer policy for this function to avoid repeated attribute
+  /// lookups in hot paths.
+  FramePointerKind FramePointerPolicy = FramePointerKind::None;
+
   /// The frame index for the stack protector.
   int StackProtectorIdx = -1;
 
@@ -641,6 +646,11 @@ class MachineFrameInfo {
   bool hasCalls() const { return HasCalls; }
   void setHasCalls(bool V) { HasCalls = V; }
 
+  FramePointerKind getFramePointerPolicy() const { return FramePointerPolicy; }
+  void setFramePointerPolicy(FramePointerKind Kind) {
+    FramePointerPolicy = Kind;
+  }
+
   /// Returns true if the function contains opaque dynamic stack adjustments.
   bool hasOpaqueSPAdjustment() const { return HasOpaqueSPAdjustment; }
   void setHasOpaqueSPAdjustment(bool B) { HasOpaqueSPAdjustment = B; }
diff --git a/llvm/lib/CodeGen/MachineFunction.cpp b/llvm/lib/CodeGen/MachineFunction.cpp
index a2dd9c425370c..71179ed9f743d 100644
--- a/llvm/lib/CodeGen/MachineFunction.cpp
+++ b/llvm/lib/CodeGen/MachineFunction.cpp
@@ -20,6 +20,7 @@
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Analysis/ProfileSummaryInfo.h"
@@ -161,6 +162,21 @@ static inline Align getFnStackAlignment(const TargetSubtargetInfo &STI,
   return STI.getFrameLowering()->getStackAlign();
 }
 
+static FramePointerKind getFramePointerPolicy(const Function &F) {
+  Attribute FPAttr = F.getFnAttribute("frame-pointer");
+  if (!FPAttr.isValid())
+    return FramePointerKind::None;
+
+  StringRef FP = FPAttr.getValueAsString();
+  return StringSwitch<FramePointerKind>(FP)
+      .Case("all", FramePointerKind::All)
+      .Case("non-leaf", FramePointerKind::NonLeaf)
+      .Case("non-leaf-no-reserve", FramePointerKind::NonLeafNoReserve)
+      .Case("reserved", FramePointerKind::Reserved)
+      .Case("none", FramePointerKind::None)
+      .Default(FramePointerKind::None);
+}
+
 MachineFunction::MachineFunction(Function &F, const TargetMachine &Target,
                                  const TargetSubtargetInfo &STI, MCContext &Ctx,
                                  unsigned FunctionNum)
@@ -202,6 +218,7 @@ void MachineFunction::init() {
   FrameInfo = new (Allocator) MachineFrameInfo(
       getFnStackAlignment(STI, F), /*StackRealignable=*/CanRealignSP,
       /*ForcedRealign=*/ForceRealignSP && CanRealignSP);
+  FrameInfo->setFramePointerPolicy(getFramePointerPolicy(F));
 
   setUnsafeStackSize(F, *FrameInfo);
 
diff --git a/llvm/lib/CodeGen/TargetOptionsImpl.cpp b/llvm/lib/CodeGen/TargetOptionsImpl.cpp
index 16d86b42db4a3..2dbde46ac62e3 100644
--- a/llvm/lib/CodeGen/TargetOptionsImpl.cpp
+++ b/llvm/lib/CodeGen/TargetOptionsImpl.cpp
@@ -10,7 +10,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/ADT/StringSwitch.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/TargetFrameLowering.h"
@@ -22,31 +21,33 @@ using namespace llvm;
 /// DisableFramePointerElim - This returns true if frame pointer elimination
 /// optimization should be disabled for the given machine function.
 bool TargetOptions::DisableFramePointerElim(const MachineFunction &MF) const {
-  const Function &F = MF.getFunction();
-
-  Attribute FPAttr = F.getFnAttribute("frame-pointer");
-  if (!FPAttr.isValid())
-    return false;
-  StringRef FP = FPAttr.getValueAsString();
-  if (FP == "all")
+  FramePointerKind FP = MF.getFrameInfo().getFramePointerPolicy();
+  switch (FP) {
+  case FramePointerKind::All:
     return true;
-  if (FP == "non-leaf" || FP == "non-leaf-no-reserve")
+  case FramePointerKind::NonLeaf:
+  case FramePointerKind::NonLeafNoReserve:
     return MF.getFrameInfo().hasCalls();
-  if (FP == "none" || FP == "reserved")
+  case FramePointerKind::None:
+  case FramePointerKind::Reserved:
     return false;
+  }
   llvm_unreachable("unknown frame pointer flag");
 }
 
 bool TargetOptions::FramePointerIsReserved(const MachineFunction &MF) const {
-  const Function &F = MF.getFunction();
-  Attribute FPAttr = F.getFnAttribute("frame-pointer");
-  if (!FPAttr.isValid())
+  FramePointerKind FP = MF.getFrameInfo().getFramePointerPolicy();
+  switch (FP) {
+  case FramePointerKind::All:
+  case FramePointerKind::NonLeaf:
+  case FramePointerKind::Reserved:
+    return true;
+  case FramePointerKind::NonLeafNoReserve:
+    return MF.getFrameInfo().hasCalls();
+  case FramePointerKind::None:
     return false;
-
-  return StringSwitch<bool>(FPAttr.getValueAsString())
-      .Cases({"all", "non-leaf", "reserved"}, true)
-      .Case(("non-leaf-no-reserve"), MF.getFrameInfo().hasCalls())
-      .Case("none", false);
+  }
+  llvm_unreachable("unknown frame pointer flag");
 }
 
 /// HonorSignDependentRoundingFPMath - Return true if the codegen must assume